JP3766694B2 - 3D reinforced ablative / thermal insulation composite - Google Patents

Description

Background of the invention High performance re-entry vehicles and critical missiles will experience heating under conditions that challenge the ablation and / or thermal insulation capabilities of conventional thermal protection materials used in them. Let's go. These conditions include a brief exposure of the thermal protection material to very high temperatures that would ablate any known material during ballistic ascent or re-entry through the atmosphere. These conditions also include prolonged exposure to relatively low heat flow levels that can raise the temperature deep inside the thermal protection material during gliding in the atmosphere, thereby reducing its thermal insulation properties. included.
In general, thermal protection materials used for high performance ballistic re-entry (eg tape-wrapped carbon phenolic resin cloth and silica phenolic resin composite) work well under ablation, but unless a large amount of insulation is used It does not have sufficient heat insulation ability to protect against overheating after prolonged heat penetration.
Traditionally, the thermal insulation ability of ablative layers of high density composite fabrics has been improved by laminating and bonding a plurality of such layers through the use of adhesives, stitching and / or reinforcing components or fasteners. It was. However, the weight of the dense ablative outer layer necessary to provide sufficient thermal insulation is generally prohibitive, so flight mission distance and / or effective to accommodate the added weight The load will be reduced.
Instead, a low density lightweight resin foam or honeycomb is laminated to the outer composite fabric heat shield layer by resin bonding to provide adequate ablation and thermal insulation protection even at light weight. Has been used as a layer. However, many of these laminates delaminated under adverse thermal conditions as would be experienced during a flight profile.
Accordingly, there is a need for ablative / insulative composites that are lighter and that have sufficient thermal protection capabilities that do not degrade (eg, delaminate) during use.
SUMMARY OF THE INVENTION The present invention relates to a three-dimensional reinforced ablative / thermal insulation composite that includes a high density fabric ablative layer and a low density resin thermal insulation layer chemically bonded to the ablative layer. The composite further includes a stitch of heat resistant yarn that passes through the ablative layer and forms a reinforcing loop within the heat insulating layer. These loops are preferably chemically and mechanically bonded to the thermal insulation layer.
The present invention has the advantage of being a lightweight material suitable for use as a heat shield against ablative heating during ballistic flight and heat permeable heating during non-ballistic flight. The present invention also has the advantage that the bond between the ablative layer and the thermal insulation layer is reinforced in multiple directions to reduce the possibility of the layers separating.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of one embodiment of a 3-D reinforced ablative / heat insulation composite of the present invention, particularly illustrating a heat resistant suture stitching reinforcement loop that enhances the bonding of the ablative layer to the heat insulation layer.
DETAILED DESCRIPTION In FIG. 1, a 3-D reinforced ablative / thermal insulation composite 10 includes a fabric-based ablative layer 12. A fabric-based ablative layer as defined herein has a material-dependent ablation resistance (depending on the heat of vaporization and the material density of the material), and generally ballistic flight (e.g., missiles) through the atmosphere. Or one or more fabrics having an overall thickness that is expected to prevent significant thermal damage to the vehicle or missile due to ablation during lift or vehicle re-entry) or non-ballistic flight (eg, glide). The ablation resistance of the ablative layer 12 is measured in terms of thickness loss or weight loss of the ablative layer 12. The ablative layer 12 is preferably completely consumed during ballistic ascent or re-entry without damaging its underlying structure (eg, vehicle or missile). Examples of fabrics with heat of vaporization suitable for the present invention include carbon fabrics and silicon-containing fabrics.
The fabric may be woven, knitted or non-woven. The fabric will preferably have a higher fiber density and thus a higher material density, as occurs with woven fabrics. More preferably, the fabric has a satin weave.
To further increase the material density, the fabric is impregnated or contains at least one non-fiber ablation resistant material that is compatible with the fabric material. Examples of such materials include carbon or cured resins such as phenolic resins, silicone resins, epoxy resins or polyimides.
For example, as described in Example 1, it is preferable to impregnate a carbon cloth with a cured phenol resin or impregnate a silicon-containing cloth with a cured silicone resin.
In a more preferred embodiment in which the ablative layer 12 contains a carbon fabric preform, the preform is applied to its interior, on fabric fibers and by means of carbon deposition and density increasing means known in the art. It further contains amorphous and / or graphitic carbon deposited in the fabric pores. Examples of such means include graphitic carbon by thermally decomposing hydrocarbons in a preform and depositing graphite using gaseous or liquid hydrocarbons, such as by chemical vapor wetting and deposition. Of deposition. Examples of means suitable for increasing the carbon density of carbon fabric preforms are detailed in Houdayer et al. US Pat. No. 4,472,454, Golkeck et al. US Pat. No. 5,348,774 and Thurston et al. US Pat.
Alternatively, the carbon fabric preform can be impregnated with a carbonizable resin (eg, epoxy resin or phenolic resin) and then carbonized to place amorphous and / or graphitic carbon in the preform. It can also be generated.
The ablative layer 12 should have a high density of usually about 1.25 g / cc or more, preferably 1.35 g / cc or more in the case of a carbon cloth-based ablative layer. In the case of a silicon-based ablative layer, the density of the ablative layer 12 is usually about 1.5 g / cc or more.
In general, the ablation resistance can be further improved by increasing the total fabric thickness in the ablative layer. However, the increase in resistance to ablation by increasing the total fabric thickness must be considered relative to the increased weight added to the missile or vehicle. In a preferred embodiment, to increase the fabric thickness of the ablative layer, the multiple layers of fabric 14 are bonded together, laminated or otherwise secured to provide a fabric stack or pre-form for use in the ablative layer 12. Make it. The fabric layers 14 are stitched together with heat-resistant yarns 16 that hardly decompose when heated to the design temperature of the composite (ie up to about 5000 ° F for ballistic flight protection or up to about 2000 ° F for non-ballistic flight protection) More preferably. Examples of suitable heat resistant yarns include carbon and silicon based yarns. As described in Example 1, the fabric layer 14 is most preferably lock stitched.
The fabric layer 14 holds the fabric layer 14 together and is sufficient to provide a path along the stitch for leakage of degradation products that form when the ablative layer 12 is exposed to high temperatures such as the ablation temperature. , Stitched with stitches per square inch of surface area. Otherwise, the cracked gas accumulated between the fabric layers 14 will cause the impregnated fabric composite to break. Generally, the fabric layers 14 are locked to each other with at least 9 stitches per square inch of surface area, more preferably at least 16 stitches per square inch. Most preferably, the stitches of the thread 16 are arranged uniformly.
For suitable ablative protection under ballistic conditions, carbon cloth is preferred as the ablative layer. This is because carbon cloth has an extremely high degree of ablative protection per unit cloth weight. The carbon fabric should have a carbon content that prevents significant thermal degradation of the fabric when exposed to an ablative temperature of about 4000 ° F to 5000 ° F. Generally, the carbon content is about 90% by weight or more. More preferably, the carbon content is about 92% by weight or more.
In general, the total fabric thickness of carbon fabric for ablative protection is about 0.01 inch to 1.0 inch. The total thickness is preferably about 0.05 inches or more. Most preferably, the total fabric thickness is about 0.3 inches to about 0.6 inches for ballistic ablative protection.
Details of the carbon cloth ballistic composite are described in Example 1.
For suitable thermal protection under non-ballistic temperature heat penetration conditions, silicon-containing cloth such as quartz cloth, silicon nitride cloth or silicon carbide cloth is preferred as the ablative layer material. Generally, the total fabric thickness of the silicon-containing fabric is between about 0.05 inches and about 1.0 inches thick, preferably between about 0.25 inches and about 0.75 inches thick. Details of the quartz cloth non-ballistic composite material are described in Example 2.
The composite also includes a plurality of heat resistant yarn stitches 18 that pass from the outer surface 20 of the ablative layer 12 through the inner surface 22 of the ablative layer 12 to form a reinforcing loop 24 outside the inner surface 22.
The purpose of the reinforcing loop 24 is to provide a three-dimensional reinforcement of the bonding of the ablative layer 12 to the thermal insulation layer 26 by providing a plurality of anchoring points that are chemically and / or mechanically coupled to the resin-based thermal insulation layer 26. That is.
The reinforcing loop 24 also preferably contains a cured thermosetting resin that is compatible with and chemically bonds to the cured resin contained in the thermal insulation layer. The number of reinforcing loops 24 provided should be sufficient to substantially prevent separation of the ablative layer 12 from the thermal insulation layer 26 under ballistic ablative conditions. This number also depends on the length of the reinforcing loop 24 disposed in the heat insulating layer 26. Generally, the composite should contain at least nine stitches 18 and reinforcing loops 24 per square inch of surface area, where reinforcing loops 24 are at least 0.05 inches long. More preferably, the composite material contains at least 16 stitches 18 and reinforcing loops 24 per square inch. Further, it is preferable that the reinforcing loop 24 is uniformly arranged in the composite material.
In a manned re-entry vehicle, the length of the reinforcing loop 24 is more preferably about 0.5 inches or longer.
The selection of a suitable thread to form the stitch 18 and the reinforcement loop 24 depends on the ability of the thread to form a stitch without breaking. The ability to form a stitch is a function of the bend radius of the yarn, and the bend radius (R) is given by the formula:
R = E × D / 2σ
Where E is the tensile rate of the yarn, D is the filament diameter and σ is the filament tensile strength. For use in suturing, it is preferred that the bend radius be about 0.005 inches or less.
In addition to having an appropriate bend radius, the yarn typically must also have sufficient filament tensile strength to break through the stitching operation without breaking. Preferably, the filament tensile strength should be about 600 ksi or greater.
When the ablative layer 12 is a carbon cloth type, a carbon yarn is preferable as a yarn used when forming the stitch 18 and the reinforcing loop 24. The carbon content of the yarn is sufficient to provide dimensional stability (ie, prevent significant separation between the ablative layer 12 and the thermal insulation layer 26) and maintain the yarn strength at the ablative temperature without material failure. There must be. In general, the carbon content of the yarn is preferably about 85% by weight or more, and the carbon content is preferably about 92% by weight or more. One preferred embodiment of the reinforcing loop 24 is discussed in Example 1.
When the ablative layer 12 is a silicon cloth type, silicon-containing yarn such as silicon nitride yarn, silicon carbide yarn or quartz yarn is preferable.
The composite 10 further includes a thermal insulation layer 26 disposed around the reinforcing loop 24 toward the inner surface of the ablative layer 12. The thermal insulation layer 26 is mechanically and / or chemically bonded to both the ablative layer 12 and the reinforcing loop 24. The thermal insulation layer 26 is preferably bonded to the reinforcement loop 24 both mechanically and chemically, as described in Example 1.
The insulation layer 26 defined herein is low enough to protect the vehicle during ablation and / or heat penetration conditions by providing a suitable degree of insulation with low weight, and material failure of the insulation It is a resin-based thermal insulating material having a sufficiently high density that can usually have the strength to prevent the above. The density is preferably about 0.2 to 0.3 grams / cc.
The low density insulation used may be of the type conventionally used as a pre-formed insulation layer in space. Suitable resins include, for example, phenolic resins, silicone resins, polyurethane resins, and epoxies that preferably bond adjacent ablative layer 12 and reinforcing loop 24 when cured to more securely bond ablative layer 12 and thermal insulation layer 26. Resin is included. If necessary to cure the resin system, an appropriate amount of resin curing agent is included.
In embodiments where the ablative layer 12 is made of carbon cloth, the preferred resin for the thermal insulation layer 26 is a phenolic resin, and as described in Example 1, a rubberized phenolic resin is more preferred.
More preferably, in order to reduce the density of the heat insulating material and at the same time improve the heat insulating capacity of the heat insulating layer 26, the heat insulating layer 26 is filled with low density such as carbon fine hollow spheres, phenol resin fine hollow spheres or glass fine hollow spheres. Also contains agents.
Most preferably, the heat-insulating layer 26 further contains fibers having a high melting point so that the strength of the layer material can be improved and a low-density heat-insulating material with improved heat-insulating ability can be used. Suitable fibers include, for example, carbon fibers, ceramic fibers and silica-based fibers as described in Example 1. The length of the fiber is preferably a few inches or less.
The thermal insulation layer 26 is a hard layer cast or machined to match the surface shape of the spacecraft or missile to which it is bonded.
The present invention is described in detail and specifically by the following examples.
Example 1
3-D reinforced ablative / insulated composite for ballistic heating conditions 3-D primarily functions as a heat shield in the ballistic atmosphere re-entry profile or to thermally protect rising assault missiles A reinforced ablative / thermal insulation composite was made from an ablative layer of carbon cloth, a thermal insulation layer of fiber reinforced phenolic resin syntactic foam, and a carbon yarn-based reinforcement.
The ablative layer was made from a carbon pre-formed layer. To produce the carbon pre-formation layer, eight layers of 90% carbonized polyacrylonitrile (PAN) satin woven fabric (19 yarns per inch x 19 yarns per inch, 0.0093 inch thickness; T300-3K fabric, Purchased from Amoco), and then tightly stitched together. The stitches used were lock stitches made from three 1320 denier carbon yarns (tensile rate of 43 million psi and tensile strength higher than 700 ksi) for both upper and bobbin yarns (lower yarns). It was.
The carbon yarn was made from 92% carbonized PAN filament (# 43 carbon filament with 4.5 micron diameter, purchased from Courtaulds). After the filament was stretched and broken, it was spun into three yarns (SA Schappe, St. Rembert, which can be spun by France).
Rock stitching was performed using a singer class 11 industrial sewing machine. Alternatively, a singer class 7 industrial sewing machine can be used. Stitches were lined up approximately 0.30 inches apart (8 stitches per inch).
A carbon yarn reinforcement was then inserted through the carbon pre-formation layer. To add the stiffener, place a pre-form layer on top of the spacer layer, and then again use three 1320 denier carbon yarns, combine them with a singer class 11 industrial sewing machine and lock stitch did. These reinforcing lock stitches penetrated the preliminary forming layer and the spacer layer from the surface of the preliminary forming layer, and were then connected to the lower thread on the lower surface of the spacer layer. The stitches were parallel to and spaced equidistantly between the rows of rock stitches used to make the carbon fabric pre-form layer (6 stitches per inch).
The spacer layer was made from three layers of 3/16 inch thick low density polypropylene foam placed on the bottom cardboard.
After inserting the reinforced lock stitch, the cardboard portion of the spacer layer was removed from the underside of the preliminary forming layer. Also, by removing this cardboard, the lower thread of the reinforced lock stitch was separated from these stitches, and a thread loop was formed that was raised from the bottom surface of the preliminary forming layer.
Next, the loops were strengthened by impregnating the loops with phenolic resin and subsequently partially curing the resin. Specifically, a phenol resin (SC1008, Borden Chemical Co.) was applied to the end of the loop (for example, by brushing or the like) and soaked into the loop. Next, the three polypropylene foam layers of the spacer layer are removed from the pre-form layer and the loop is stiffened by heating the phenolic resin to state B (partially cured) for about 5 minutes in a 250 ° F. air circulating oven. Thereby forming a reinforcing loop.
Next, a fiber reinforced phenolic resin syntactic foam insulation layer was formed in place, i.e., around the reinforcement loop toward the lower surface of the pre-formation layer. First, 211 grams of phenolic resin micro hollow sphere (No. 0930, purchased from Union Carbide) was dry blended with 35 g of 1/8 inch long shredded quartz fiber (JPS Glass Fabrics) using compressed air. A substantially uniform dry mixture. The dry mixture was then mixed with 50 grams of 5% rubber modified phenolic resin and 60 grams of methanol was added as a solvent to produce a processing phenolic resin mixture or wet mixture.
The 5% rubber modified phenolic resin was prepared by mixing an appropriate amount of 1008 phenolic resin and rubber modified phenolic resin (Schenectady Chemicals type HRJ-1387, acrylonitrile-butadiene rubber). Due to this rubber modification, the heat insulating layer was reduced in brittleness and became tougher.
The phenolic resin mixture was then troweled onto the reinforcing loop and the pre-formed layer surface to form an uncured phenolic resin layer. Subsequently, the uncured phenolic resin layer is cured in a vacuum bag under a reduced pressure of about 14 psi while being heated in an oven at about 350 ° F. for about 8 hours, thereby forming a fiber reinforced phenolic resin syntactic foam heat insulating layer. I let you. During the curing process, which is a condensation reaction of the phenolic resin, the syntactic foam solidifies around the inner surface of the carbon preform and around the carbon loop. In this way, the thermal insulation layer becomes denser as its reaction products, methanol and bubbles are removed from the phenolic resin layer and between the pre-formation layer and the phenolic resin layer by decompression and its exposed surface. Becomes more flat.
After curing, the thermal insulation layer was machined to the desired thickness.
Subsequently, the preliminary forming layer is impregnated with a phenol resin (SC1088), and after the resin is brought into the B state, compression molding is performed to further strengthen the cloth in the preliminary forming layer, thereby forming a high-density ablative layer. At the same time, the ablative layer was fabricated from the carbon pre-formed layer by chemically bonding the ablative layer to the heat insulating layer.
Compression molding is performed in a hydraulic press by placing a heated platen on the pre-formed layer and a water-cooled platen against the insulation and then pressing the platen together in the press to about 200 psi. A -D reinforced ablative / thermal insulation composite was formed. The water-cooled platen was cooled to minimize the decomposition of the thermal insulation layer.
Analysis of this composite revealed that the ablative layer had a high density of about 1.37 grams / cc and a fiber volume of about 60%, while the density of the thermal insulation layer was about 0.23 grams / cc.
From the evaluation of the area of this composite containing reinforced loops, which were sliced and microscopically examined, the loops were mechanically well embedded in the foam insulation and were partially curved in the loops in advance. It was found that the cured (state B) resin was also chemically bound in the foam microstructure because it was bound to the resin in the phenolic resin layer at the loop / syntactic foam interface when the thermal insulation layer was cured. It was.
Example 2
3-D reinforced ablative / thermal insulation composite for heat penetration conditions A composite for use under long-term heat penetration conditions as experienced during atmospheric gliding was fabricated by the method described in Example 1. . However, the ablative layer was made using 10 layers of quartz cloth (model number 581; JPS glass Fabrics), which was made with quartz sewing thread (Quartz Products continuous filament 300-2 / 8 thread) and lock stitched together. . This stitch has a stitch row of 8 stitches per inch with a row spacing of 0.25 inch.
The stitches used to make the reinforcing loop were the same stitch pattern. The loop was reinforced with a hard silicone resin (glass resin GR908F type, Owens-Illinois).
The composition of the insulating foam layer was 60% silicon micro-hollow sphere (Grace Syntactics), 7% 1/8 inch chopped quartz fiber and 33% RTV silicone elastomer.
Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be included within the scope of this invention as set forth in the following claims.

Claims (16)

a) High density cloth-based ablative layer;
b) a plurality of heat yarn stitch, wherein said stitch passes through the ablative layer, and the stitches form a reinforcing loop outside of the inner surface of the ablative layer; and c) a low density resin-based thermal insulation layer , wherein the heat-insulating layer is formed around the loop, bonded to the inner surface of the ablative layer, wherein the loop is embedded in the heat insulating layer,
A three-dimensional reinforced ablative / thermal insulation composite comprising A ) a multi-layered fabric in which dense fabric-based ablative layers are arranged in a stack;
Claim 1 comprising and c) non-fibrous resistance Abure Deployment of capital material disposed within fabric preforms; that binds b) fabric layers together to form a fabric preform, coupling means The composite material described. The composite of claim 2, wherein the coupling means comprises a plurality of lock stitches made in resistant thermal yarn. The composite of claim 2, wherein the fabric preform includes multiple layers of carbon fabric. The composite of claim 4, wherein the non-fibrous resistance Abure Deployment of capital material disposed within preform comprises further a cured carbon-containing resin. The composite material according to claim 5, wherein the hardened carbon-containing resin contains a phenol resin. The composite of claim 4, wherein the non-fibrous resistance Abure Deployment of capital material disposed within preform is a carbon. The composite of claim 3, wherein resistance heat yarn is carbon fiber. The composite of claim 1, wherein the heat resistant yarn is selected from the group consisting essentially of carbon yarn, quartz yarn, silicon nitride yarn and silicon carbide yarn. The composite of claim 1, wherein the thermal insulation layer comprises a) a cured resin; and b) a fine hollow sphere. The composite of claim 10, wherein the cured resin is selected from the group consisting essentially of phenolic resins, rubber- modified phenolic resins, silicone resins, epoxy resins and polyimide resins. 11. The composite material according to claim 10, wherein the fine hollow sphere is selected from the group consisting essentially of a phenol resin fine hollow sphere, a carbon fine hollow sphere, and a glass fine hollow sphere. Furthermore, the composite material of Claim 10 containing a high temperature fiber. The composite of claim 13, wherein the high temperature fibers are selected from the group consisting essentially of carbon fibers, ceramic fibers and silica fibers. 3D reinforced ablative / thermal insulation composite for thermal protection from ablation,
a) a high density ablative layer containing multiple layers of carbon cloth, wherein the cloth also contains a cured phenolic resin;
b) a plurality of carbon yarn stitches, wherein the stitches pass through the ablative layer and the stitches form a reinforcing loop outside the inner surface of the ablative layer; and c) of the syntactic rubber modified phenolic resin foam A three-dimensional reinforced ablative / thermal insulation composite comprising a low density thermal insulation layer, wherein the foam comprises fine hollow spheres and high temperature fibers. A three-dimensional reinforced ablative / thermal insulation composite for thermal protection under heat penetration conditions,
a) a high density ablative layer containing multiple layers of quartz cloth, wherein the cloth also contains a cured silicone resin;
b) a plurality of quartz yarn stitches, wherein the stitches pass through the ablative layer and the stitches form a reinforcing loop outside the inner surface of the ablative layer; and c) a low density thermal insulation layer of syntactic silicone foam Wherein the foam comprises a three-dimensional reinforced ablative / thermal insulation composite comprising fine hollow spheres and high temperature fibers.

Images